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(FMFBV-ALG
(NAME "fmfbv") ; FM feedback unit generator
(ARGUMENTS ("time_type" "t0") ("double" "hz") ("rate_type" "sr")
("sound_type" "index"))
(START (MIN index))
(TERMINATE (MIN index))
(LOGICAL-STOP (MIN index))
(STEP-FUNCTION index)
(STATE ("double" "yy" "0.0")
("double" "sin_y" "0.0")
("double" "phase" "0.0")
("double" "ph_incr" "hz * SINE_TABLE_LEN / sr;
index->scale *= SINE_TABLE_LEN / PI2
"))
(INNER-LOOP "phase += ph_incr;
if (phase > SINE_TABLE_LEN) phase -= SINE_TABLE_LEN;
/* PHASE is incremented and INDEX scaled to table INDEX, and
sin_y is a signal (-1 to +1) */
yy = phase + index * sin_y;
/* so yy is a table index */
while (yy > SINE_TABLE_LEN) yy -= SINE_TABLE_LEN;
while (yy < 0) yy += SINE_TABLE_LEN;
sin_y = sine_table[(int) yy]; /* truncation gets valid index */
/* sin_y is now a signal ready for table lookup */
output = sin_y")
(CONSTANT "ph_incr")
(SAMPLE-RATE "sr")
(SUPPORT-HEADER "#include \"sine.h\" /* sine_table and SINE_TABLE_LEN */
")
)
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